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Run your home on clean, sustainable electricity simply by harnessing the power of flowing water. Using low-impact mechanical systems, a home-scale hydroelectric system (or "microhydro") mobilizes the kinetic energy of water gushing downhill from a stream or river, then directs it onto a wheel in a turbine that converts the rotational energy to electricity.

If you have at least 2 gallons per minute of flowering water, a good amount of drop, shelter from bad weather, and permission from the relevant authorities-that's important, even if the project is on your own land-you can build your own microhydro system. Expect to part with $1,000 for the smallest setup to $20,000 for a system large enough to power several modern homes. ::Mother Earth News

Difficulty level: Advanced